Support nasm coff obj format for djgpp

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
diff --git a/configure.ac b/configure.ac
index 235d271..67e53cf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -163,6 +163,7 @@
 	*-*-cygwin|*mingw*) OBJ_FORMAT=win32 ;;
 	*-*-darwin*) OBJ_FORMAT=macho ;;
 	*emx*) OBJ_FORMAT=aout ;;
+	*djgpp) OBJ_FORMAT=coff ;;
 	*) OBJ_FORMAT=elf ;;
 esac
 AC_SUBST(OBJ_FORMAT)